CVE-2021-34484
CVE-2021-34484 is a security flaw in Microsoft Windows, Microsoft’s operating system for PCs and servers. Someone who already has a foothold can use Microsoft Windows to take full control of the machine. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 31 Mar 2022.[1]
Microsoft Windows is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Fixed in version 10.0.10240.19022, 10.0.14393.4583, 10.0.17763.2114 and 10.0.18363.1734 and others.
Description
CISA calls it an user profile service privilege escalation in Microsoft Windows. In its words: “Microsoft Windows User Profile Service contains an unspecified vulnerability that allows for privilege escalation.”[1]
The underlying weakness is improper privilege management (CWE-269), in MITRE’s list of common software weaknesses.[2]
It scores 7.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Windows 10 Version 1507 | 10.0.10240.19022 |
| Windows 10 Version 1607 | 10.0.14393.4583 |
| Windows 10 Version 1809 | 10.0.17763.2114 |
| Windows 10 Version 1909 | 10.0.18363.1734 |
| Windows 10 Version 2004 | 10.0.19041.1165 |
| Windows 10 Version 20H2 | 10.0.19042.1165 |
| Windows 10 Version 21H1 | 10.0.19043.1165 |
| Windows 7 | 6.1.7601.25685 |
Every device with Microsoft Windows needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 31 Mar 2022, 231 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 21 Apr 2022 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 22%. That’s in the top 3% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Microsoft has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Update Microsoft Windows now.On Windows: Settings, Windows Update, Check for updates, then restart. Office updates come the same way, or from any Office app: File, Account, Update Options. Then turn on automatic updates, so the next fix arrives on its own.
- Check you’re on 10.0.10240.19022 or later.Fixed in version 10.0.10240.19022, 10.0.14393.4583, 10.0.17763.2114 and 10.0.18363.1734 and others. Anything older is what attackers are going after.
- If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 22%.[4] |
See also
Other Microsoft Windows flaws
- CVE-2026-96951: command injection ·
- CVE-2026-85880: heap-based buffer overflow ·
- CVE-2026-81963: link following ·
- CVE-2008-4250: buffer overflow ·
- CVE-2026-32202: protection mechanism failure ·
- CVE-2025-60710: link following ·
Other improper privilege management flaws
- CVE-2026-102490, Zammad GmbH Zammad: improper privilege management ·
- CVE-2026-84869, ConnectWise ScreenConnect: improper privilege management and missing authorization ·
- CVE-2026-46817, Oracle E-Business Suite: improper privilege management ·
- CVE-2024-8068, Citrix Session Recording: improper privilege management ·
- CVE-2023-28434, MinIO: security feature bypass ·
Added the same day
- CVE-2022-26871, Trend Micro Apex Central: arbitrary file upload ·
- CVE-2022-1040, Sophos Firewall: authentication bypass ·
- CVE-2021-28799, QNAP Network Attached Storage (NAS): NAS improper authorization ·
- CVE-2021-21551, Dell dbutil Driver: insufficient access control ·
- CVE-2018-10562, Dasan Gigabit Passive Optical Network (GPON) Routers: GPON routers command injection ·
Every Microsoft flaw on CISA’s list · Everything added in March 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Windows User Profile Service Privilege Escalation Vulnerability”. Known Exploited Vulnerabilities Catalog, added 31 Mar 2022.
- ^ National Institute of Standards and Technology. “CVE-2021-34484 Detail”. National Vulnerability Database, published 12 Aug 2021.
- ^ Microsoft. Advisories and fixes: msrc.microsoft.com, portal.msrc.microsoft.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.218, percentile 97.6, 31 Oct 2026.
- CVE Program. “CVE-2021-34484”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.